How to modify the initial ssthreshold in NS3?

[shux...@gmail.com]

Hi, I have ran the demo "fifth.cc" in the directory "/example/tutorial". I found that tcp is in the state of slow start phrase before retransmitting. The congestion window(cwnd) is always increasing if without dropping a packet. Now I intend to modify the  initial slow start threshold to a smaller value that I could see the congestion avoidance phrase before retransmit appearing.  But I found the value of m_initialSsThresh in the class of TcpSocketBase is set to zero, I don't know why? My objective is to generate a tcp stream that contains the phrases of slow start, congestion avoidance, fast retransmit, so I need to know:

1. How to set the initial slow start threshold value?

2. How to replace the tcp protocal? for example, tcp new reno replace the cubic.

Thank you.

[Tommaso Pecorella]

Hi,

the answer is... an attribute of ns3::TcpSocket:

    .AddAttribute ("InitialSlowStartThreshold",
                   "TCP initial slow start threshold (bytes)",
                   UintegerValue (UINT32_MAX),
                   MakeUintegerAccessor (&TcpSocket::GetInitialSSThresh,
                                         &TcpSocket::SetInitialSSThresh),
                   MakeUintegerChecker<uint32_t> ())

Check the manual for details on attributes.

About how to change the TCP flavour, check the examples in the examples folder.

T.